Wave 150i RA Hysteresis v. PPEC

[NY2KW]

Last night was one of the first clear nights at a remote site (SFRO) to compare which would give me the best guiding.  Previously I ran guiding with tracking at the celestial equator and meridian with Dec near 0° for 30 min and analyzed the Guide Log and found my mount's period was 287 sec. I then ran Guiding Assist and accept its recommendations.  Last night I started with those settings again, ran Calibration Assistant. Then watched it guide with RA Hysteresis for about 40 min.  My total rms error ranged between 0.46" -0.55".  It was the best I have ever seen with this mount but seeing was great with lowest HFR around 1.70.  I stop guiding, switched to PPEC and let it run for almost an hour.  Looking at the last 15-20 minutes, the best total was around 0.75-0.85".      I switched back to Hysteresis algorithm and let it run for about 20 min then started my imaging session which began with M106 to the north.  Guiding soon went haywire.  I had to abort, tried to rerun Guding Asst but it failed to complete.  I ried to go through all the logs- PHD2, GSS, NINA and I was lost.  I uploaded the logs to ChatGPT, described the problem and it discovered that immediately prior to the loss of guiding, NINA had finished slewing to the trarget and rotated my camera.  My guide is with an external guidescope not OAG .  ChatGPT pointed out that my PHD2 profile allowed the CAA to connect andf PHD2 was expecting the rotation as affecting my guide camera as if it were an OAG.  I changed my prfile and hope that tonight all will go well.  The scope is already guiding near the celestial equator/meridian at 0.50".  I had the tech staff check my scope today (I left it in the last position) for any cable or mechanical snags and none were found.  I looked at the PHD2 manual and its not very clear that for non-OAG guiding that connecting to the rotator may cause these kinds of problems. 

[NY2KW]

My apologies for not including the log.  Here it is

https://openphdguiding.org/logs/dl/PHD2_logs_MgMe.zip

[Bruce Waddington]

If you're not guiding with an OAG, then the guide camera isn't being rotated when the rotator for the imaging camera is moved.  So your PHD2 configuration profile should not include a connection to the rotator.  

We have tried to make this clear in both the User Guide and the new-profile-wizard but maybe we have come up short:

User Guide:

PHD2 does not control a rotator, but it will read the current angle setting from the rotator and adjust the guiding calibration if needed.  Rotators are used to control the orientation of the imaging camera with respect to the sky - perhaps to keep the orientation the same on opposite sides of the pier or to create a favorable composition of the objects in the field of view.  If the rotator is part of an off-axis-guider assembly, its rotation will affect the PHD2 calibration.  In this situation, PHD2 should be connected to the rotator so the calibration can be adjusted automatically.

New-profile-wizard:

So, perhaps we should extend the sentence in the User Guide to say "otherwise, you should not connect PHD2 to the rotator".

The point of all this is that PHD2 has to know the angular orientation of the guide camera relative to the sky - that's the only way it can translate the X/Y movements of the guide star on the camera sensor into the RA/Dec movements of the mount axes.  It's essentially a transformation from the X/Y coordinate system of the camera sensor into the RA/Dec coordinate system of the mount and the nighttime sky.

With regard to the RA tracking errors you are looking at, the session beginning at 22:43 shows some fairly nasty problems.  Here is a look at the unguided RA tracking during that period. 

 If you look at the errors identified by the red arrows, you can see there are some rather abrupt large errors - errors of many arc-sec that occur during intervals of a minute or less.  This is not typical periodic error which usually produces a relatively smooth sine-wave pattern.  Abrupt errors like this are going to be hard to guide out.  It would be good if you could get some help from the manufacturer of your mount to see if you can get improvements via mechanical adjustment.  Sometimes, these kinds of problems can be caused by a drive system that is too tightly meshed.

Regards,

Bruce

[Brian Valente]

NY2KW

just for clarity, can you send pic or two of your system, including the image train and guiding setup?

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[NY2KW]

Thank you Bruce and Brian for the quick replies.  Here is last nights session.  I began by erasing the previous calibration and running Calibration Asst again.  Conditons last night were much worse than the night before, i.t high clouds, high humidity and the remote roof had to be closed early at around 02:47a.  Here is the link to last night's log:  https://openphdguiding.org/logs/dl/PHD2_logs_SAYq.zip.  Also here is a picture my setup at the remote site.

[Brian Valente]

Do you have a picture from the opposite side? the guiding setup and the CAA is blocked by the ASIAir and filter wheel. If you have to ask them for additional pic, please have them take a few from different angles.

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